I'm continuing with my surreptitious commentary on ejh's puzzles to try out the "elements" identified by Levitt and Friedgood (2008) - see comment to puzzle #1 for more. This one also scores on Geometry I think - look at those bishops (btw would it matter if the black ones were on b2 and b3? If not, then Heathcote must have put them on a1 and a2 for prettiness). Also a bit of Paradox maybe: that backward key move, and the seeming irrelevance of the Ba1/WKh8 battery. "Paradox. Surprise, outrageousness. An immediate confrontational tension is created...the response might be 'How can this be possible?' or 'That simply cannot work!'" So, a bit of Paradox, but not much more than any other 2-mover, maybe.